This invention relates to a process for producing olefin polymers and to a high activity catalyst suitable for use in the process.
It is old in the field of olefin polymerization to prepare solid polyolefins by employing catalyst systems comprising a transition metal compound and an organometallic cocatalyst. Until fairly recently most of such catalyst systems were relatively low in activity and as a result generally required the employment of a catalyst removal step in order to obtain a polymer having satisfactory properties. Recently, however, much research has been directed toward the discovery of catalyst systems that are so active that there is no need to employ the catalyst removal step. Such catalyst systems are obviously of significant commercial importance since they allow for appreciable reductions in the costs of producing such polymers.
Included among the early relatively low activity catalysts were systems involving the use of a vanadium halide, an aluminum halide, and an organophosphorus compound. See for example the catalyst systems disclosed in U.S. Pat. No. 2,969,345 and U.S. Pat. No. 3,186,977. It has been noted that when a vanadium halide, an organoaluminum halide, and an organophosphorus compound are combined in the polymerization diluent as taught by those patents, an intractable oily or gummy form of catalyst is produced. While this might not present too much of a problem if the polymerization were conducted at temperatures under which the polymer is substantially dissolved, for modern particle form polymerization wherein the polymer is produced in solid form, it would lead to serious fouling of the reactor. For a particle form polymerization, it would obviously be more desirable, if not absolutely necessary, to have the catalyst in the form of individual solid particles. It was further noted that the activity of the catalysts of the two aforementioned patents was not nearly high enough to produce polymer in such quantity that subsequent catalyst removal could be eliminated.
The present invention is based upon the discovery of a way to produce a solid vanadium-containing catalyst capable of producing ethylene polymers in such amounts that the catalyst removal step is generally unnecessary.